<PAGE>   1

                                                                    Exhibit 2.18

                   FIRST AMENDMENT TO ASSET PURCHASE AGREEMENT

         THIS FIRST AMENDMENT TO ASSET PURCHASE AGREEMENT (this "AMENDMENT") is
made and entered into as of the 28th day of June, 2000, by and among CHARTER
BEHAVIORAL HEALTH SYSTEMS, LLC, a limited liability company duly organized under
the laws of the State of Delaware ("CHARTER"), CHARTER BEHAVIORAL HEALTH SYSTEM
OF MANATEE PALMS, LP and CHARTER BEHAVIORAL HEALTH SYSTEM AT MANATEE ADOLESCENT
TREATMENT SERVICES, LP ("CHARTER SUBS"), CHARTER ADVANTAGE, LLC, a wholly-owned
subsidiary of Charter and a limited liability company duly organized under the
laws of the State of Delaware ("CHARTER ADVANTAGE"), and CHARTER MANAGED CARE
SERVICES, LLC, a wholly-owned subsidiary of Charter and a limited liability
company duly organized under the State of Delaware ("CHARTER MANAGED CARE")
(with Charter, Charter Sub, Charter Advantage, and Charter Managed Care being
collectively referred to as "THE CHARTER ENTITIES"), and RAMSAY YOUTH SERVICES,
INC., a corporation duly incorporated under the laws of the State of Delaware
("BUYER") (with The Charter Entities and Buyer referred to individually as a
"PARTY" and collectively as the "PARTIES").

                              W I T N E S S E T H:

         WHEREAS, the Parties have entered into that certain Asset Purchase
Agreement dated May 19, 2000, pursuant to which Buyer is obligated to purchase
and the Charter Entities are obligated to sell the Purchased Assets related to
operation of the Facilities known as Manatee Palms, Manatee Adolescent Treatment
Services and the Kingsley Center (the "PURCHASE AGREEMENT");

         WHEREAS, the Parties desire to amend the Purchase Agreement;

         NOW, THEREFORE, for and in consideration of the premises, the mutual
promises and covenants contained herein, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto hereby agree as follows:

1. CAPITALIZED TERMS. Capitalized Terms contained in this Amendment which are
not defined herein shall have those meanings assigned to them in the Purchase
Agreement.

2. AMENDMENT OF PURCHASE AGREEMENT. The Purchase Agreement is hereby amended as
follows:

         A. Section 1.1(a) shall be removed, and shall be replaced in its
entirety with the following:

         "(a) all of the Charter Entities' rights, title and interests in, to
         and under those certain equipment, machinery and vehicle leases,
         service agreements, third party payor agreements, or other contracts,
         agreements or commitments related to the Facilities or the Business
         that Buyer has elected to assume in accordance with the provisions of
         this Section 1.1(a) and Section 1.2 (the "CONTRACTS"), with a list of
         such assumed Contracts attached hereto as EXHIBIT B; provided, however,
         that the Buyer shall be solely responsible for all costs of curing such
         assigned Contracts. Notwithstanding anything contained in this Section
         1.1(a) or in Section 1.2 to the contrary, Buyer shall not be obligated
         to take an assignment of any of the contracts identified on Exhibit B
         if the cure amount is unresolved as of the date of this Amendment. For
         those contracts as to which the cure amount is unresolved, the Charter
         Entities shall provide written notification to Buyer of the cure amount
         as soon as practicable, and Buyer shall have five days after receipt of
         such notice to provide written notice to the Charter Entities as to
         whether Buyer will take an assignment of such contract."

         B. Section 1.2 shall be removed, and shall be replaced in its entirety
with the following:


<PAGE>   2

                  "1.2 ASSUMED CONTRACTS/PERMITS. The Charter Entities shall
                  take all action reasonably necessary in order to assume and
                  assign the Contracts listed on EXHIBIT B to the Buyer, or its
                  designees, in accordance with Sections 365(a) and (f) of the
                  Bankruptcy Code, and shall pay all costs associated with such
                  assumption and assignment, except any costs to cure such
                  Contracts. Upon Bankruptcy Court Approval (defined below),
                  which order shall include provisions authorizing the
                  assumption and assignment of the Contracts, such Contracts
                  shall be assumed by the Charter Entities and assigned to the
                  Buyer, or its designees, contemporaneously with the Closing
                  (defined below) and such assumption and assignment shall be
                  effective as of the Closing. Additionally, the Charter
                  Entities shall assign all Permits, to the extent permitted by
                  law and necessary to the conduct of the Business to the Buyer.
                  Four of the Contracts set forth on EXHIBIT B, (including (1)
                  F8014 FL-DJJ High/Moderate Risk Female Program at Kingsley
                  Center, (2) F7019 FL-DJJ MATS Halfway House - 50 Beds, (3)
                  F7027 FL-DJJ CBHS Manatee Palms - 35 Beds Sexual Offender, (4)
                  F7024 FL-DJJ Level 2 and Aftercare Services), as amended, are
                  critical revenue producing contracts (the "Critical
                  Contracts"), and represent a material part of this
                  transaction. Buyer shall have the right, pursuant to paragraph
                  8.1, to immediately terminate this Agreement if any of the
                  Critical Contracts terminates prior to the Closing Date, or if
                  the Charter Entities are unable to assume and assign to Buyer
                  any of the Critical Contracts as of the Closing Date. In such
                  event, Buyer shall be entitled to a refund of the Deposit
                  pursuant to paragraph 8.3."

         C. The following shall be added to the end of Section 2.1:

                  "The Deposit shall be placed in an escrow account with First
                  Union National Bank, and the fees and expenses incurred
                  establishing or maintaining such escrow account shall be paid
                  equally by Charter and Buyer."

         D. The last two sentences of Section 3.1 shall be removed, and shall be
replaced in their entirety with the following:

                  "Notwithstanding the previous sentence, the Closing Date must
                  occur on or before July 20, 2000. If the Closing does not
                  occur by July 20, 2000, then this Agreement shall terminate
                  automatically in accordance with Section 8.1, unless Buyer and
                  the Charter Entities mutually agree in writing to extend the
                  Closing Date."

         E. Section 8.1(g) shall be removed in its entirety, and shall be
replaced with the following:

                  "(g) this Agreement shall automatically terminate if the
                  conditions in Section 6.3 hereof are not satisfied by July 20,
                  2000, or such other date as the Buyer an d the Charter
                  Entities mutually agree in writing; and"

         F. Section 8.1(h) shall be removed in its entirety, and shall be
replaced with the following:

                  "(h) this Agreement shall automatically terminate in the event
                  that the Closing does not occur by July 20, 2000, for any
                  reason other than


<PAGE>   3

                  those state in (a) through (g) above, unless Buyer and the
                  Charter Entities mutually agree in writing to extend the
                  Closing Date."

         G. The following shall be added to Section 8.1 as new Section 8.1(h),
and the existing Section 8.1(h) shall be renumbered as Section 8.1(i):

                  "(h) this Agreement may be immediately terminated by Buyer, if
                  any of the Critical Contracts identified in paragraph 1.2 of
                  this Amendment terminates prior to the Closing Date, and may
                  be terminated by Buyer if the Charter Entities are otherwise
                  unable to assume and assign to Buyer any of the Critical
                  Contracts as of the Closing Date.

         H. Section 8.3 shall be removed, and replaced in its entirety with the
following:

                  "REFUND OF DEPOSIT. Charter will refund to Buyer the amount of
                  the deposit actually paid by Buyer to Charter under Section
                  2.1, if this Agreement is terminated or terminates
                  automatically under Sections 8.1(a), 8.1(c), 8.1(e), 8.1(f),
                  8.1(g), or 8.1(h). If this Agreement is terminated for any
                  reason other than termination or automatic termination under
                  Section 8.1(a), 8.1(c), 8.1(e), 8.1(f), 8.1(g), or 8.1(h),
                  Buyer will forfeit the Deposit, and, in addition, when Buyer
                  receives the refund of its deposit of $87,600 being held
                  pursuant to the Real Estate Purchase Agreement with Crescent,
                  Buyer shall remit such $87,600 refund to Charter."

         I. The following shall be added below the designation "CHARTER SUBS" of
EXHIBIT A:

                  "Charter Behavioral Health System of Manatee Palms, LP Charter
                  Behavioral Health System at Manatee Adolescent Treatment
                  Services, LP"

         J. EXHIBIT B shall be removed, and shall be replaced in its entirety
with the list of contracts attached hereto as "EXHIBIT B."

         K. EXHIBIT C shall be removed, and shall be replaced in its entirety
with the list of Allocation of Purchase Price attached hereto as "EXHIBIT C."

         L. SCHEDULE 4.1(i) shall be removed.

2. PURCHASE AGREEMENT IN FULL FORCE AND EFFECT. The Parties acknowledge and
agree that the Purchase Agreement, as amended by this Amendment, is in full
force and effect.

3. MISCELLANEOUS.

         A. INTERPRETATION. This Amendment shall not be construed more strictly
against either party hereto regardless of which party is responsible for its
preparation, it being agreed that this Amendment was fully negotiated by both
parties.


<PAGE>   4

         B. HEADINGS. The titles, captions and headings contained in this
Amendment are inserted for convenience of reference only and are not intended to
be a part of or to affect in any way the meaning or interpretation of this
Amendment.

         C. BINDING EFFECT. This Amendment shall be binding upon and shall inure
to the benefit of the parties and their respective heirs, representatives,
successors and permitted assigns.

         D. GOVERNING LAW. This Amendment shall be governed by and construed in
accordance with the laws of Delaware, without regard to the principles of
conflicts of laws.

         E. COUNTERPARTS; FAX SIGNATURES. This Amendment may be executed in one
or more counterparts, each of which shall be deemed to be an original, but all
of which together shall constitute the same agreement. Any signature page of any
such counterpart, or any electronic facsimile thereof, may be attached or
appended to any other counterpart to complete a fully executed counterpart of
this Amendment, and any telecopy or other facsimile transmission of any
signature shall be deemed an original and shall bind such party.

         F. 0ENTIRE AGREEMENT. This Amendment, and the Purchase Agreement,
together with all Exhibits, Appendices and Schedules to the Purchase Agreement
contain the entire agreement and understanding concerning the subject matter
hereof between the parties and specifically supersedes any other agreement or
understanding among the parties related to the subject matter hereof.

         G. TIME IS OF THE ESSENCE. Time is of the essence for this Amendment.

         IN WITNESS WHEREOF, the undersigned have caused their respective duly
authorized representatives to execute this Amendment as of the day and year
first above written.

                                            CHARTER BEHAVIORAL HEALTH
                                            SYSTEMS, LLC

                                            By:
                                               ----------------------------
                                            Name:
                                                 --------------------------
                                            Title:
                                                  -------------------------

                                            CHARTER BEHAVIORAL HEALTH SYSTEM OF
                                            MANATEE PALMS, LP

                                            By:
                                               ----------------------------
                                            Name:
                                                 --------------------------
                                            Title:
                                                  -------------------------


<PAGE>   5

                                            CHARTER BEHAVIORAL HEALTH SYSTEM AT
                                            MANATEE ADOLESCENT TREATMENT
                                            SERVICES, LP

                                            By:
                                               ----------------------------
                                            Name:
                                                 --------------------------
                                            Title:
                                                  -------------------------

                                            CHARTER ADVANTAGE, LLC

                                            By:
                                               ----------------------------
                                            Name:
                                                 --------------------------
                                            Title:
                                                  -------------------------

                                            CHARTER MANAGED CARE SERVICES, LLC

                                            By:
                                               ----------------------------
                                            Name:
                                                 --------------------------
                                            Title:
                                                  -------------------------

                                            RAMSAY YOUTH SERVICES, INC.

                                            By:
                                               ----------------------------
                                            Name:
                                                 --------------------------
                                            Title:
                                                  -------------------------